The present invention relates to a method of causing abrasive grains to collide against and contact with an object being treated to form surfaces of the object into a matte. Specifically, a rotational magnetic field is applied on magnetic abrasive grains to cause the same to vibratingly move at random to collide against and contact with an object being treated to obtain a matte. More specifically, the invention is applied on finishing of an aluminum pipe for electrophotographic photosensitive body.
Conventionally, the dry shot blasting method and the wet shot blasting method have been used for matte treatment of an object being treated. These methods cause jet of a working fluid, for example, compressed air, or acceleration of a medium with the use of an impeller to cause the same to collide against an object being treated to finish surfaces of the object being treated. However, there is a need of supplying a medium, separating a medium made fine due to collision, replenishing a medium, or the like, which requires a large-scaled equipment. In order to solve such problem, a method has been disclosed, in which an object being treated is received in a vessel, which is filled with abrasive grains and possesses gas permeability, and compressed air from an air nozzle with a tip end thereof directed toward the object being treated is jetted toward the object being treated to perform surface treatment of the object being treated (Japanese Provisional Patent Publication No. 78995/1974). However, only effects of not much more than descaling, derusting can be expected of such methods.
Meanwhile, a method has been disclosed, in which a rotational magnetic field is applied (Japanese Provisional Patent Publication No. 227755/1995). With such method, a permanent magnet or a direct current electromagnet are mounted on a doughnut-shaped yoke to be rotated, and when the method is applied on magnetic abrasive grains charged in a surface treatment vessel, magnetic abrasive grains are put together in a chain manner to be taken along and rotated with rotation of magnetic poles while being attracted to surfaces of the surface treatment vessel (in many cases, serving also as an object being treated) by magnetic forces, thus rubbing surfaces of the object being treated, so that even if surfaces of the object being treated are polished and smoothed, effects of much more than that cannot be expected.
Further, methods making use of a rotational magnetic field includes a method, in which AC voltage is applied on a rotational magnetic field generating device formed in a motor/stator manner (Japanese Provisional Patent Publication No. 2001-138207). With such method, magnetic abrasive grains are not put together in a chain manner but is made independent one by one, and magnetic poles change in a very short time in one location, so that magnetic abrasive grains vibratingly move at random to collide against and contact with an object being treated to make surfaces of the object a matte. Therefore, the method appears at a glance to be valuable as a matte treatment method for surfaces of an object being treated, but it exceedingly detracts efficiency in terms of utilization of a rotational magnetic field and exceedingly degrades a commercial value because no account is taken of that blackening phenomenon of surfaces of an object being treated, caused due to the fact that fine powder of an object being treated is generated as the surface roughening treatment proceeds and the fine powder remains in the vessel as it is. Further stated, no account is taken to obtain uniformity of quality in the case of industrial application.
Also, when applied repeatedly to the electromagnetic type surface roughening method in an ordinary manner, magnetic abrasive grains are gradually increased in residual magnetic forces, which impede vibratory move at random to make it difficult to obtain a desired surface roughness.
Further, in the case where aluminum or aluminum alloy drawn tubes are used as a substrate for electrophotographic photosensitive body, there is a need of rough cutting and finishing cutting prior to application of the dry shot blasting method or the wet shot blasting method. Cost for finishing cutting accounts for a major part of cost for treatment, and so a demand for cost reduction is pressing.